From the late 1970s through the present day the use of digital computing devices has proliferated in businesses, homes, academia, and a multitude of other environments. This development has been due, in large part, to a continuing increase in the speed at which computers retrieve and process large amounts of information. Nevertheless, because the complexity of tasks performed by computers continues to increase, there remains a further need to accelerate the speeds at which computers operate.
Computers comprise three principal component types, which allow them to receive, store, manipulate and transmit data. These principal component types are peripheral, processor and memory. Peripheral devices transmit information into and out of a computer. Processors are the workhorses of a computing device, recalling and manipulating information as instructed by a controlling program. The memory devices store processed and inputted information as well as programming instructions for the processors.
These components act in concert with one another to carry-out the computing process. Because of this, the slowness of one component necessarily acts as a speed governor on the entire computing process. Memory is the slowest principal component, and thus the speed governor of the computing process. Thus, there exists a need in the art for memory devices of improved speed.
The most commonly used memory devices are two basic types, random access and disk drive. While random access type memory provides fast access times, it is expensive to maintain and volatile, loosing information when power is removed. As a result, random access memory is unsuitable for long term storage of the bulk of information use by a computer, which must be retained over long terms. Therefore, typical random access memory is normally used for storage of executable program instructions, buffers for holding data recently processed, awaiting processing, when generally expected to be used in the relatively near future, and buffers for input/output devices, including display memory. Because of this, disk drive memory, which is non-volatile and relatively inexpensive, is used for the long term storage of information.
While typical disk drives provide economical devices for storing relatively large amounts of information, access to that information tends to be slow as compared to the speeds at which a computer CPU can process information and information can be written to and from random access memory. Thus, the rate limiting step for many processes executed by general purpose digital computer is often the time required to retrieve data from a disk or write it to a disk.
In particular, a parameter of a disk drive is the access time. The access time is the time lag between the issuance of a call for reading data from a disk until the data is actually available at the port to which the disk is attached. The components of the access time are the seek time plus the maximum time to locate the first information of interest on a particular track. These parameters are generally specified as worst case parameters. Thus, the seek time is the maximum time required to move the typical movable head assembly of a disk drive from one position to another, normally across the entire radial width of the disk. The balance of the access time is the time required for the disk to make almost a full revolution since worst case analysis requires assuming that the head arrives at the appropriate track just after the first bit position of interest is passed under it and thus must await almost a full revolution of the media before the data of interest passes under the head. In modern disk drive systems, particularly those used in small personal computers, seek time is on the order of tens of milliseconds, while instruction execution speed is normally on the order of a few nanoseconds. Thus, the need to obtain data from a disk drive can be viewed as slowing down operation of the computing device by a factor on the order of a million.
Over the last decade, applications programs for small computers have become more and more complex, and provide for the storage and manipulation of very large amounts of data. In particular, relational database programs for storing large numbers of relatively large records are in common use. Many such applications unavoidably cause the computer running them to perform many disk reads and writes during processing of records of performing tasks that require access to multiple records, such as report generation. In many such applications, the time required for disk accesses determines the speed at which a particular task can be performed, and no increase in CPU performance can significantly improve the overall result.
Typically, a disk drive comprises a set of vertically stacked media disk (also termed platters), a set of read/write heads mounted to actuator arms and a motor for rotating the media disk relative to the read/write heads. The media disks are circular with two horizontal faces that are opposite and parallel to each other. The media disks are rotatably mounted on a spindle connected to the motor such that the media disks rotate in unison. Thus, the set of disks geometrically defines a cylinder with the mounting spindle defining a longitudinal main access of the cylinder and the access of rotation of the individual disks.
The horizontal faces of the media disks are each coated with a magnetically permeable film, which is subdivided into concentric tracks. The tracks are logically divided into a plurality of magnetized bit positions for storing information. Information is stored in the tracks by aligning magnetic fields at the bit positions to particular patterns. Those patterns can later be read to reproduce the information stored.
Bit fields are aligned by magnetic fields generated by the read/write heads. The read/write heads each comprise a core element wrapped by a wire coil. A magnetic field is generated by passing a current through the wire coil. Because the polarity of the field is dependent on the direction of the current flow, the magnetic field may by reversed by alternating the direction of the current through the coil. This ability allows information to be stored by aligning bit fields into one of two possible orientations.
The actuator arms radially move the read/write heads inwardly and outwardly over the media disks. The read/write heads float on a cushion of air generated by the rotation of the media disk. When information is stored to a media disk, a read/write head is moved over the media disk, the desired track in which the information is to be stored is located. Current is then passed through the coil of the read/write head as necessary to generate the magnetic fields that align the bit fields of the track in the desired pattern. Similarity, when information is recalled from the media disk, a read/write head is moved over the media disk to the desired track in which the information is stored and the alignments of the bit fields of the track are read by the induced currents in the head coil.
Due to the amount of information contained in most computer files, more than one track is required to store most files. Thus, most files are stored to various tracks, which may or may not abut each other. To store or retrieve a file, then, the actuator arm must typically move the read/write head back and forth between multiple tracks, accessing one track at a time. In so doing, a relatively large amount of time is lost due to inertia in positioning the read/write head over the different tracks and to accessing only one track at a time.
As noted above, access times for disk drives are the rate limiting step in full execution of many applications that require intensive use of disk storage. Furthermore, more complex applications are sometimes written with program overlays so that they may be run on computers with somewhat limited amounts of addressable random access memory. An overlay is a portion of the executable code of a program that can be written into or out of memory, under the control of the main portion of the program that always stays resident in memory during program execution, in order to accommodate different tasks at different times. Overlays are written into the memory for executable code from a disk file. Therefore, the calling of multiple routines that require overlays to be written into memory is inherently slow because of the time required to fetch the overlay from the disk drive and read it into system memory.
In summary, the power and speed of general purpose digital computers made today allows very complex tasks to be performed. As the processing speed of the machines increases, the complexity of the tasks asked of them by the authors of application programs have tended to likewise increase. The increase in the complexity of the task in the amount of data to be manipulated has caused a corresponding increase in the number of disk accesses typically required for complex data processing tasks. Since the disk access time is many orders of magnitude slower than typical CPU processing time, typical slow disk drives have acted as something of an anchor on the overall goal of increased throughput of data processing by modern general purpose computers. Thus, there is a need in the art for an economical disk drive system, particularly for a small computer, with greatly reduced access times.
Prior art fixed head magnetic data storage media have been built and proposed. One of the earliest mass storage devices used with computer systems were rotating cylindrical drums coated with magnetizable oxides some of which included an array of fixed heads over the recording surface. Those multi fixed head systems are shown, for example, in U.S. Pat. Nos. 3,090,947 and 3,320,599. No prior art system known to the inventors has provided a practical fixed head arrangement for implementing a high density hard disk drive of the type typically used in small general purpose computers today. No system for the present invention has provided a practical implementation of a fixed head disk drive that is suitable for a high density small track width disk drive with storage capacity and bits per unit area commensurate with that available for modern conventional movable head technologies.
Another development in disk drive technology in recent years has been the increased density of data storage per unit area of the storage media. Closer head to media spacings, more than the availability of more precision stepping motors do control head positioning have lead to significant increases in the amount of data that can be stored on given size rotating medium. Typically, increased density is achieved by smaller track widths which in turn require more precision positioning for the heads during read and write operations.
As track widths and inter tracks facings become smaller, greater attention must be paid to phenomenon such as thermal expansion and contraction of the media disk, similar thermal phenomenon on head carriage mechanisms, and a particular differential co-efficients of expansion between the media disk and the apparatus carrying the movable head assembly. Since the head carriage and moving apparatus is typically made from different materials than the substrate carrying the magnetizable media, they tend to expand and contract with different thermal coefficients thus leading to problems of misalignment as a thermal phenomenon.
The closely spaced tracks of high density disks require the read/write heads to be very accurately positioned over the tracks so that the heads do not incorrectly access information of a wrong but closely spaced track. Thus, there exists a need in the art for an accelerated disk drive with means for accurately maintaining the position of the read/write heads over the tracks of high density disks.
Another problem associated with high density disk drives is that the read/write heads must be mounted in extreme close proximity to the magnetic film. This is because a weaker, more precise magnetic field must be used in accessing a track of a high density disk in order to prevent the bits of adjacent tracks from being affected. A result of such mounting, however, is that normal wear and tear or slight fluctuations during disk access may cause the read/write heads to impact the magnetic film of the media disk (also termed a crash) and by that cause a catastrophic failure of the disk drive. Therefore, there exists a need in the art for an accelerated high density disk drive with means for safely mounting the read/write heads in close proximity to the media disks.